1. Field of the Invention
The present invention pertains to hardware-in-the-loop testing of millimeter wave tracking and guidance systems and, more particular, to a technique for controlling the position of a simulated target for such testing.
2. Description of the Related Art
A need of great importance in military and some civilian remote sensing operations is the ability to quickly detect and identify objects, frequently referred to as “targets,” in a “field of regard.” A common problem in military operations, for example, is to detect and identify targets, such as tanks, vehicles, guns, and similar items, which have been camouflaged or which are operating at night or in foggy weather. It is important in many instances to be able to distinguish reliably between enemy and friendly forces. As the pace of battlefield operations increases, so does the need for quick and accurate identification of potential targets as friend or foe and as a target or not.
Remote sensing techniques for identifying targets have existed for many years. For instance, in World War II, the British developed and utilized radio detection and ranging (“RADAR”) systems for identifying the incoming planes of the German Luftwaffe. RADAR uses radio waves to locate objects at great distances even in bad weather or in total darkness. Sound navigation and ranging (“SONAR”) has found similar utility and application in environments where signals propagate through water, as opposed to the atmosphere. While RADAR and SONAR have proven quite effective in many areas, they are inherently limited by a number of factors. For instance, RADAR is limited because of its use of radio frequency signals and the size of the resultant antennas used to transmit and receive such signals. Sonar suffers similar types of limitations. Thus, alternative technologies have been developed and deployed.
Some of these alternative technologies are optical in nature. One such alternative technology is laser detection and ranging (“LADAR”). Similar to RADAR systems, which transmit and receive radio waves to and reflected from objects, LADAR systems transmit laser beams and receive reflections from targets. Because of the short wavelengths associated with laser beam transmissions, LADAR data exhibits much greater resolution than RADAR data. Typically, a LADAR system creates a three-dimensional (“3-D”) image in which each datum, or “pixel”, comprises an (x,y) coordinate and associated range for the point of reflection. However, some optical systems operate two-dimensionally. Optical systems can be used for automatic target recognition, targeting, direction finding, and other, similar tasks.
Such tracking and guidance systems are typically expensive to design and build, even in prototype. Furthermore, they are usually designed to operate over relatively long distances and frequently at high speeds. New designs are therefore tested by simulation. Hardware-in-the-loop (“HWIL”) simulations for RF missile seeker guidance verification requires simulated target angle motion in synchronization with the missile motion simulator in order to evaluate intercept performance. Target angle motion control has classically been achieved with either mechanical x-y positioners or exotic electronic implementations to achieve the desired results. Mechanical positioners are costly and have limited coverage and acceleration, high losses, poor phase stability, and low reliability. Classical exotic electronic techniques use amplitude and phase control at lower frequencies with up-conversion to millimeter wave (“MMW”) for each element. This is expensive and requires extensive calibration.
More particularly, missile tracking and guidance systems are typically tested during development in an anechoic chamber. The guidance system prototype is placed at one end of the anechoic chamber. The wall of the chamber at the opposite end is honeycombed with antennas, sometimes referred to as “horns.” The antennas are controlled in groups of three referred to as “triads,” to radiate energy in a pattern that will simulate the presence of a target. More particularly, each horn of the triad radiates a signal, and the three signals interfere with each other at a desired point. The desired point is in the two-dimensional, triangular space defined by the triad. To simulate movement of the target within the triad, the radiated energy can be controlled to “move” the simulated target within the triad. Movement can be simulated outside of a given triad, but within the honeycomb pattern as a whole, by forming new triads and controlling their radiated energy similarly. Because the simulated target's position is defined within the triad whose signal's generate it, the target cannot be simulated at a position outside the physical dimensions of the honeycomb of antennas.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.